Space-VLBI phase-reference mapping and astrometry

We present 5 GHz space-VLBI observations of the quasar pair B1342+662/B 134 2+663 that demonstrate the feasibility of phase-reference techniques using an antenna in space. The space-based data were taken by the satellite HALCA , of the space-VLBI mission VSOP. From residual (referenced) phases we deri ve an upper bound of 10 meters to the uncertainty of the spacecraft orbit r econstruction. An analysis of the phase-reference maps of the sources addit ionally suggests that the above mentioned uncertainty is likely not larger than 3 meters. With errors of this magnitude, HALCA is a useful tool for as trometric studies of close pairs of radio sources.